Nagumo is a very skilled assassin but it’s fair to say that he would not last very long against someone like Pegasus Seiya. Seiya is just on another level and could end the planet in an instant if he really wanted too. Nagumo has no real answer for that kind of power and would not have the speed needed to dodge any of his attacks as well. That is why he would ultimately be doomed here. Pegasus Seiya wins.